1. Field of the Invention
The present invention relates generally to fluid flow meters and, more particularly, to a fluid flow meter in which the fluid flow range can be easily varied.
2. Description of the Prior Art
There have been a number of previously known fluid flow meters having a housing with a fluid inlet, a fluid outlet and means for measuring and exteriorly indicating the fluid flow from the inlet and to the outlet. For example, in one type of previously known fluid flow meters, a semicircular vane cooperates with a hemispherical shaped housing disposed between the fluid inlet and the fluid outlet. Rotation of the vane provides a variable size opening between the vane and the housing while resilient means urges the vane towards a closed position. The rotation of the vane within the housing, caused by the fluid flow into the housing inlet, is used to provide an exteriorly visible signal of the vane rotation and, thus, of the fluid flow rate through the housing.
In a still further type of fluid flow meter, a tapered needle cooperates with a port which fluidly connects the inlet to the outlet. In addition, a piston is axially slidably mounted within the housing and secured to either the tapered needle or the port so that the displacement of the piston caused by the fluid flow through the flow meter variably opens the port in dependence upon the flow rate. Electrical and/or mechanical indicating means are attached to the piston member to provide a signal of the axial displacement of the piston and hence of the fluid flow rate through the flow meter.
One disadvantage of these previously known flow meters is that the flow range for the flow meter is preset and nonadjustable after assembly of the flow meter. Consequently, if a different flow range for the flow meter is desired, it is necessary to replace the entire flow meter.